Communications system using adaptive filter circuit using parallel adaptive filters

ABSTRACT

A communications system receives a modulated communication signal that carries encoded communications data. A signal input receives the communication signal. An adaptive filter circuit is connected to the signal input and comprises N number of parallel adaptive filters. Each adaptive filter has non-adaptive and adaptive taps with weighted coefficients that are different in number from the respective other parallel adaptive filters within the adaptive filter circuit. A selection output circuit is connected to each adaptive filter and selects for output the adaptive filter having the most suppression or least output power or other criterion which can indicate a best choice to use of the N parallel adaptive filters. A demodulator demodulates the signal and a decoder receives the filtered output signal from the demodulator and decodes the signal to obtain the communications data.

FIELD OF THE INVENTION

The present invention relates to communications, and more particularly,the present invention relates to adaptive filters used in communicationssystems to reduce signal interference due to intentional orunintentional narrowband jammers.

BACKGROUND OF THE INVENTION

Radio communication channels such as HF, VHF and UHF introducedistortion in the form of multipath and fading into the originallytransmitted signal. A result of these types of channels is inter-symbolinterference (ISI), which occurs if the modulation bandwidth exceeds thecoherent bandwidth of the radio channel and causes the modulation pulsesto spread in time to adjacent symbols. Intersymbol interference can alsobe caused by the radio channel exhibiting time and frequency dispersion(e.g., delay spread and Doppler spread) due to the presence of signalreflectors/scatterers in the environment or the relative motion oftransmitter and receiver. Intersymbol interference has also been knownto cause bit errors at the receiver, which distorts the intended messagecontent. To address such transmission channel distortion, many differenttypes of channel estimation algorithms and adaptive equalizers have beenincluded in the receivers.

Modern communication systems are requiring wider and wider bandwidthsignals in order to support the data rates desired by users. The largeamount of legacy equipment in the HF/UHF/VHF bands can at times causeunintentional interference to these new wideband systems. In addition,intentional jamming can also occur. Adaptive filters are commonly usedin communication systems to reduce the effects of narrowbandinterferers. An adaptive filter can process the communication signalprior to acquisition, demodulation, equalization and decoding. Adaptivefilters do not require knowledge of the channel in advance andincorporate an Infinite Impulse Response (IIR) or Finite ImpulseResponse (FIR) filter with adaptive filter coefficients that adjustthemselves to achieve a desired result, such as minimizing unwantednarrowband interference of the input signal. The adaptive filtertypically uses an adaptive Recursive Least Squares (RLS), Least MeanSquares (LMS) or Minimum Mean-Square Error (MMSE) estimation as analgorithm.

Modern communication systems typically transmit a preamble (i.e. a knownwaveform section) which demodulators can use to achieve waveformsynchronization. In addition, the preamble may also contain informationtransmitted in a very robust fashion used to indicate the waveformparameters used for the data portion of transmission that follows thisinitial preamble (i.e. modulation type (2-PSK, 4-PSK, 8-PSK, 16-QAM,etc), burst length, type of forward error correction, etc). When asystem incorporates waveform information in its preamble it is referredto as an autobaud system. When another mechanism is used to convey thisinformation, such as a control channel or a separate transmissionproviding this information, the preamble is used only forsynchronization. It may be advantageous to a communication system tofeedback demodulator state (preamble search state, preamble state, anddata state) and demodulator information (modulation type, etc) toadaptive filter to more effectively deal with narrowband interferencewhile reducing the effects of adaptive filter on the data portion ofwaveform.

There are many design tradeoffs when using adaptive filters in modernwideband UHF/VHF tactical radios such as number of filter taps, speed ofadaptation, etc. In addition, many platform (i.e. radio hardware)constraints such as size, weight, power and relatively small FieldProgrammable Gate Array (FPGA) usage are imposed on the adaptive filterdesign. The proper tradeoff in the adaptive filter design is necessaryso that more than one interferer can be handled by adaptive filter(typically three to four is desired) while still meeting platformconstraints. Examples of interferers in the HF/VHF/UHF band are analogfrequency modulation (FM) voice, frequency shift keying (FSK) signals(i.e. 16 kbps FSK), tone signals or carriers.

Some adaptive filters incorporate spectral based techniques that use aFast Fourier Transform (FFT), thus, making them too complex for someradio implementations. Adaptive filters such as Finite Impulse Response(FIR) filters, or Infinite Impulse Response (IIR) filters exist and havebeen found to work well at lower bit rates and bandwidths. Both types offilters, however, have some drawbacks, but with improvements, shouldprovide important design enhancements for adaptive filters used incomplex communications systems.

SUMMARY OF THE INVENTION

A communications system receives a modulated communication signal thatcarries encoded communications data. A signal input receives thecommunication signal. An adaptive filter circuit is connected to thesignal input and comprises N number of parallel adaptive filters. Eachadaptive filter has non-adaptive and adaptive taps with weightedcoefficients that are different in number from the respective otherparallel adaptive filters within the adaptive filter circuit. Aselection output circuit is connected to each adaptive filter andselects for output the adaptive filter having the most suppression orleast output power or other criterion which can indicate a best choiceto use of the N parallel adaptive filters. A demodulator demodulates thesignal and a decoder receives the filtered output signal from thedemodulator and decodes the signal to obtain the communications data.

In one aspect the communications system has each adaptive filterincluding a power measuring circuit for measuring the power output fromeach adaptive filter. The adaptive filters can have an increasing numberof adaptive taps starting from a first adaptive filter having oneadaptive tap, the next adaptive filter having two adaptive taps, up to Nadaptive taps for nth adaptive filter. At least one of the adaptivefilters also includes a normalizing circuit on the input to filterand/or on the output of filter that obtain sample values from a receivedsignal to increase the gain recovery based on the type of modulationused by communication system, the demodulator state such as preamblesearch, preamble detection, data state and/or other signal acquisitioninformation.

In yet another aspect of at least one of the adaptive filters includesan interference reduction circuit responsive to one of at least thereceived state of the demodulator, the type of modulation used by thecommunication system, the demodulator state such as preamble search,preamble detected and data state and/or other signal acquisitioninformation, the power measured at the input of adaptive filter, and thepower measured at the output of adaptive filter for updating theadaptive gain of the adaptive filter, separating the spacing of themultipath introduced by adaptive filter, controlling input and outputnormalizing circuits to adaptive filter and selecting if the signalpassed to the demodulator is the original received signal or signaloutput by the adaptive filter. At least one of the adaptive filters alsoincludes a variable delay circuit operative before the adaptive filtertaps for separating the spacing and multipath introduced by the adaptivefilter and producing a filtered output signal with improved multipathperformance and reduction of narrowband interference.

In yet another aspect at least one of the adaptive filters includes anadaptive gain circuit for updating the adaptive gain of the adaptivefilter responsive to a received state of a demodulator or the type ofmodulation used by communication system.

In another aspect, at least one of the adaptive filter outputs can beselected to be sent to the demodulator if it is determined that adaptivefilter is benefiting the received waveform and if determined thatadaptive filter is not benefiting waveform the original received signalcan be sent to demodulator instead.

An adaptive filter and method is also set forth.

BRIEF DESCRIPTION OF THE DRAWINGS

Other objects, features and advantages of the present invention willbecome apparent from the detailed description of the invention whichfollows, when considered in light of the accompanying drawings in which:

FIG. 1 is a block diagram showing basic signal processing modules orcomponents used in a conventional receiver that incorporates ademodulator, equalizer and decoder.

FIG. 2 is a block diagram of an adaptive filter in accordance with anon-limiting example of the present invention.

FIG. 3 is a block diagram showing a plurality of adaptive filters inparallel each having a different number of adaptive taps such that thefilter with smallest output power or most suppression or other criterionis selected as an output.

FIGS. 4A through 4C show graphs for the effect of the update gain onGaussian noise input for respective gains of ½⁷, ½³ and ½¹⁰ inaccordance with a non-limiting example of the present invention.

FIGS. 5A through 5C show the effect of the update gain on Gaussian noiseand a tone (20 dB) input for respective gains of ½⁷, ½³ and ½¹⁰ inaccordance with a non-limiting example of the present invention.

FIGS. 6A through 6C show the effect of update gain on a GMSK (GaussianMinimum Shift Keying) signal input with respective gains of ½⁷, ½³ and½¹⁰ in accordance with a non-limiting example of the present invention.

FIGS. 7A through 7C show the effect of update gain on a GMSK signal anda tone (20 dB) input with respective gains of ½⁷, ½³ and ½¹⁰ inaccordance with a non-limiting example of the present invention.

FIG. 8 is a graph showing the effect of the update gain on the GMSKsignal and tone (20 dB) input, and showing the settling time with theupdate gains of ½⁷, ½³ and ½¹⁰ in accordance with a non-limiting exampleof the present invention.

FIGS. 9A through 9D show the effect of the number of adaptive taps onthe GMSK signal and the tone (20 dB) input with the various suppressionsat 16.87, 18.19, 18.79 and 19.22 dB in accordance with a non-limitingexample of the present invention.

FIG. 10 is a block diagram of an example of a communications system thatcan be used in accordance with a non-limiting example of the presentinvention.

FIG. 11 is a high-level block diagram showing basic components that canbe used in accordance with a non-limiting example of the presentinvention.

FIG. 12 is a perspective view of a portable wireless communicationsdevice as a handheld radio that could incorporate the communicationssystem and adaptive filter in accordance with a non-limiting example ofthe present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Different embodiments will now be described more fully hereinafter withreference to the accompanying drawings, in which preferred embodimentsare shown. Many different forms can be set forth and describedembodiments should not be construed as limited to the embodiments setforth herein. Rather, these embodiments are provided so that thisdisclosure will be thorough and complete, and will fully convey thescope to those skilled in the art. Like numbers refer to like elementsthroughout.

The different embodiments as will be explained below describe anadaptive filter as a narrow band interference (NBI) filter. Although anadaptive Finite Impulse Response (FIR) filter is preferred, the adaptivefilter could be formed as an Infinite Impulse Response (IIR) filter. Inone embodiment, an additional variable delay between the fixed andadaptive taps is included. This delay improves multipath performance bymaking the multipath resolvable for the channel estimation algorithmsand equalizers used in demodulator circuit. Because the input power ofthe adaptive filter relative to the output power of the adaptive filteris a good indicator of interference suppression, this power can bemeasured and information fed back to control a variable delay before theadaptive taps and to control an automatic tap order selection circuit.

A large single interferer or jammer is often best handled by one or twotaps (less taps reduces ISI introduced by adaptive filter), and inaccordance with a non-limiting example of the present invention, thenumber of taps can be chosen or updated to accommodate signal changes,such as the appearance of a large interferer or jammer. The adaptivefilter uses the state of the receive modem (i.e. demodulator) to selectan adaptive update gain, while a variable delay is placed between thefixed and adaptive taps. An automatic application of the adaptive filtercan be based on the measured output power by bypassing the adaptivefilter or selecting the output of the adaptive filter. The tap orderselection can be based automatically on the modulation of the dataportion of waveform and the adaptive filter state. The variable adaptivegain can be based on the demodulator state such as the preamble search,preamble, data and also on the waveform modulation of data portion ofwaveform.

The communications system includes an adaptive filter to provide anenhancement for automatically selecting whether to use the adaptivefilter output and automatically determining the optimum number ofadaptive filter taps based on the adaptive filter performance and themodulation of the data portion of waveform. The adaptive filter canadjust its update gain based on the demodulator state and adjust thevariable delay before the adaptive taps to improve the modem performancebased on feedback from demodulator.

The communications system uses the adaptive filter, in accordance with anon-limiting example of the present invention, to remove narrow bandinterferers or jammers for many different wideband waveforms, overcomingthe disadvantages that occur when a standard handheld radio is withinrange of a wideband receiver and disrupts reception. A wideband waveformcould be a key differentiator of newer manpack and handheld radios, andthe adaptive filter, in accordance with a non-limiting example of thepresent invention, can work advantageously in real tactical radioenvironments.

Selected non-limiting parameters can include a gain with the variablesof ½⁷, ½³ and ½¹⁰, and the total number of taps can vary from as few asone to about 3 to 6 in a non-limiting example. The number of adaptivetaps can vary from 1 to 4 in another non-limiting example. The systemprovides multiple, delayed taps (spaced at the symbol rate of modulatedwaveform) that are adaptive after a first fixed tap in one embodimentand an automatic in/out filter selection based on the output power ofthe adaptive filter. The order or number of taps can be automaticallyselected based on the output power of the adaptive filter. An adaptiveupdate gain can be based on the receive state of the modem, includingthe search, preamble and data and the modulation such as GMSK (GaussianMinimum Shift Keying), BPSK (Binary Phase Shift Keying), QPSK(Quadrature Phase Shift Keying), M-PSK (M-ary Phase Shift Keying) andM-QAM (M-ary Quadrature Amplitude Modulation, i.e. 16-QAM).

It should be appreciated by one skilled in the art that the approach tobe described is not limited for use with any particular communicationstandard (wireless or otherwise) and can be adapted for use withnumerous wireless (or wired) communications standards such as EnhancedData rates for GSM Evolution (EDGE), General Packet Radio Service (GPRS)or Enhanced GPRS (EGPRS), extended data rate Bluetooth, Wideband CodeDivision Multiple Access (WCDMA), Wireless LAN (WLAN), Ultra Wideband(UWB), coaxial cable, radar, optical, etc. Further, the invention is notlimited for use with a specific PHY or radio type but is applicable toother compatible technologies as well.

Throughout this description, the term communications device is definedas any apparatus or mechanism adapted to transmit, receive or transmitand receive data through a medium. The communications device may beadapted to communicate over any suitable medium such as RF, wireless,infrared, optical, wired, microwave, etc. In the case of wirelesscommunications, the communications device may comprise an RFtransmitter, RF receiver, RF transceiver or any combination thereof.Wireless communication involves: radio frequency communication;microwave communication, for example long-range line-of-sight via highlydirectional antennas, or short-range communication; and/or infrared (IR)short-range communication. Applications may involve point-to-pointcommunication, point-to-multipoint communication, broadcasting, cellularnetworks and other wireless networks.

As will be appreciated by those skilled in the art, a method, dataprocessing system, or computer program product can embody differentexamples in accordance with a non-limiting example of the presentinvention. Accordingly, these portions may take the form of an entirelyhardware embodiment, an entirely software embodiment, or an embodimentcombining software and hardware aspects. Furthermore, portions may be acomputer program product on a computer-usable storage medium havingcomputer readable program code on the medium. Any suitable computerreadable medium may be utilized including, but not limited to, staticand dynamic storage devices, hard disks, optical storage devices, andmagnetic storage devices.

The description as presented below can apply with reference to flowchartillustrations of methods, systems, and computer program productsaccording to an embodiment of the invention. It will be understood thatblocks of the illustrations, and combinations of blocks in theillustrations, can be implemented by computer program instructions.These computer program instructions may be provided to a processor of ageneral purpose computer, special purpose computer, or otherprogrammable data processing apparatus to produce a machine, such thatthe instructions, which execute via the processor of the computer orother programmable data processing apparatus, implement the functionsspecified in the block or blocks.

These computer program instructions may also be stored in acomputer-readable memory that can direct a computer or otherprogrammable data processing apparatus to function in a particularmanner, such that the instructions stored in the computer-readablememory result in an article of manufacture including instructions whichimplement the function specified in the flowchart block or blocks. Thecomputer program instructions may also be loaded onto a computer orother programmable data processing apparatus to cause a series ofoperational steps to be performed on the computer or other programmableapparatus to produce a computer implemented process such that theinstructions which execute on the computer or other programmableapparatus provide steps for implementing the functions specified in theflowchart block or blocks.

For purposes of description, there is now described a prior artcommunication system relative to FIG. 1, which schematically illustratessignal processing modules or steps of a conventional receiver thatincorporates basic components. Referring to FIG. 1, the receiver 20includes an antenna 22 for receiving the signal, a radio receiver filter24 for limiting the bandwidth of the incoming signal (3 KHz for an HFsignal as an example), a digital down-converter 26 for converting asignal from a 1800 Hz carrier to baseband (for an HF signal), a digitallow pass filter 28, a demodulator 30 (with one or more equalizer), adeinterleaver 32, and a decoder 34 for forward error correction. Blockinterleavers and de-interleavers typically have several different userselectable lengths to allow selection of proper block size for currentchannel conditions. In accordance with non-limiting examples, filteringcould occur prior to demodulation and equalization.

It should be understood that an adaptive filter uses the characteristicsof the input signal. Typically, the adaptive filter, for example, anadaptive FIR filter, has a self-learning process and the adaptivealgorithm is selected to reduce the error between the output signal anda desired signal. One algorithm as mentioned before is the Least MeanSquares (LMS) algorithm that approximates the steepest descent algorithmto use an instantaneous estimate of a gradient vector of a costfunction. It should be understood that other algorithms such as RLS orMMSE algorithms can be used. For description, the LMS algorithm isdescribed as a non-limiting example.

In the LMS algorithm, the estimate of the gradient is based on samplevalues of a tap-input vector and an error signal. The algorithm iteratesover each coefficient in the filter, moving it in the direction of theapproximated gradient. The LMS performance achieves its minimum valuethrough the iterations of the adapting algorithm and the adaptive filteris finished when the coefficients converge to a solution such that theoutput from the filter matches the desired signal. When the input datacharacteristics such as the filter environment are changed, the filteradapts to the new environment by generating a new set of coefficientsfor new data.

When the LMS algorithm is used in an equalizer structure, the LMSalgorithm uses a reference signal representing the desired filter outputand the difference between the reference signal and the output of thefilter is an error signal. Thus, the LMS algorithm finds a set of filtercoefficients that minimizes the expected value of a quadratic errorsignal to achieve the least mean squared error. In many systems, thesquared error is a quadratic function of the coefficient vector andthere is typically a global minimum and no local minima.

Thus, the filter changes or adapts its parameters in response to changesin the operating environment such that the output can track a referencesignal with minimum error as coefficients are changed. The equalizer canbe operated in a training mode and a tracking mode. Channelcharacteristics can be learned for a first time in a training mode,while in the tracking mode, the characteristics of the channel arefollowed, assuming they do not change quickly. A specially chosentraining signal could be applied to the channel input and is presumed tobe known to the equalizer. In a tracking mode, while actualcommunication occurs, the signal is unknown to the equalizer.

In accordance with a non-limiting example of the present invention, FIG.2 illustrates a block diagram of an adaptive filter 43 for use invarious examples of the present invention. Although the filter isillustrated as a Finite Impulse Response (FIR) Filter, it can bedesigned as an Infinite Impulse Response (IIR) filter. The adaptivefilter 43 includes an input X(n) 44 and appropriate delay elements 45a-c (illustrated as three delay elements) and four weighted taps 46 a-dand outputs that are summed within a summer 47. Other delay elementswith appropriate weighted coefficients can possibly be used. A fixed tap45 is included as illustrated before adaptive taps and could include oneor more fixed taps, typically one. The output Y(n) 48 from the summer 47is subsequently received within a receiving modem 49.

In accordance with a non-limiting example, a variable delay circuit 50is incorporated between fixed and adaptive taps as illustrated. Theinput 44 is also passed through an input normalizer circuit 51 that canbe controlled by a control processor 51 a before reaching the variabledelay circuit 50. An automatic tap order selection circuit 52 isincorporated within the filter as well as a variable update gain circuit53. From the summer 47, the output 48 is passed through an outputnormalizer circuit 54, which can be controlled by the control processor51 a, and an output power measuring circuit 55 a. Input power can bemeasured at an input power measuring circuit 55 b. A power based switch56 at the output allows the input signal 44 to be switched eitherdirectly to the receiving modem 49 or through the adaptive filter bymeans of a bypass channel 58.

The receiving modem 49 can include a feedback channel 57 a to carryinformation concerning the multipath tolerances of the modem andinformation about the amount of multipath back to the variable delaycircuit 50. The power based switch 56 allows switching between thefilter and the input as illustrated. Modem state information asexplained below is fed back through a feedback channel 57 b to thevariable update gain circuit 53. The power measuring circuit 55 a feedsback information regarding the power output from the filter to the powerbased switch 56 and the automatic tap order selection circuit 52 throughfeedback channel 57 c. Input power as measured by power measuringcircuit 55 b is fed to the automatic tap order selection circuit 52 andpower based switch 56.

A delay can be provided between the fixed and adaptive taps to improvemultipath performance and make the multipath resolvable. Because theinput power and output power of the filter is a good indicator of theinterference suppression, the filter can be automatically applied basedon the output power while automatic tap order selection occurs based onmodulation used for data and the filter state. The power based switchpermits automatic selection of the signal path either through the filteror through a bypass channel 58 to an output 59 as illustrated. Thefilter also automatically determines an optimum number of adaptive tapsdependent on the filter performance and modulation and can adjust theupdate gain of the filter based on the modem state, data modulation,etc.

The variable delay circuit 50 makes the multipath more discernable anddifferentiates multipath when it is next to each other by separating themultipath because the equalizer function as a whole tends to performbetter if there is greater spacing between the multipath (as long asmultipath does not exceed multipath capability of equalizer or channelestimation algorithms). The automatic tap order selection circuit 52recognizes that it is possible to perform the job with a required numberof taps, for example, one or two taps, which may be better suited fordifferent jamming or interfering signals. It is possible to select oneor the other or more, or any combination. This structure and function isadvantageous if the system is attempting to remove one or two differentjamming signals. Thus, the minimum number of taps can be usedeffectively.

The power measuring circuit 55 feeds back power information into theautomatic tap order selection circuit 52, allowing the number of taps tobe chosen based on the power output of the filter. Power is a goodmetric or indicator of how well the filter is working and how muchsuppression is actually obtained. This can be obtained by measuring theratio of the output power to the input power, giving an indicatorwhether the filter is removing jammers. It is possible to look at theserelative powers and decide which one of the taps (filters), such as theone or two taps, is the best one to choose.

The variable update gain circuit 53 permits updating of the taps byobtaining feedback of demodulator state information from the receivingmodem through the feedback channel 57 b. This information allows anadaptive update gain based on the received state of the modem (i.e.whether demodulator is in the preamble search state, preamble state anddata state) and the type of modulation used to carry data, such as GMSK,BPSK, QPSK, M-PSK and M-QAM.

As noted before, the power based switch 56 switches the signal betweenthe bypass and the filter output. For example, if the output power isabout the same as the input power, the filter is not accomplishing anyreal suppression and the switch is operable such that the signal isbypassed into the top bypass channel 58 from the input through the powerbased switch 56 and output to the receiving modem 49. If the filter isoperative as measured by the ratio of output power and input power usingthe power measuring circuit 55, the input signal is switched through thefilter 43 and into the output 48 of the summer 43 and through thenormalizer 54 and power measuring circuit 55. This switching functioncan be advantageous because even when the filter is not accomplishingmuch suppression, the waveform and any noise at the taps will stillcause the taps to “jump” or move even a small amount and there is stillsome distortion imparted to the received signal. Thus, a high-leveldecision can occur whether the filter should be used or not.

As to the demodulator state information that is fed back to the variableupdate gain circuit 57 through the channel 57 b, it is possible tooperate the filter with different gains or different internals dependingon the state of the demodulator. Typically, a demodulator will searchfor a waveform and will run with a particular updated gain functionwhile searching. Once the waveform is detected, it might be possible toslow down the adaptation rate so that the system does not overmodulateor severely distort the received signal. The amount of “jumping” by thetaps is decreased. For example, it is possible to run at first with alarger gain (i.e. faster adaptation), but once a signal is acquired, thegain can be made smaller (i.e. slower adaptation by using a smallergain) so there will be less noise enhancement from the adapting filtertaps.

The variable delay 50 at the front end of the adaptive filter 43 givessome separation to the multipath. The feedback from the modem allowsinformation regarding the receiving modem's multipath tolerances and theamount of multipath and allows an adjustment in the delay such that themultipath will not become so large in its separation and extend beyondthe functional multipath capability of the receiving modem 49.

In the system for each input, sampley(n)=x(n)−w1*x(n−2−v)−w2*x(n−3−v)−w3*x(n−4−v)−w4*x(n−5−v). Taps areupdated with each sample w(i)=w(i)+k*x(n−i)*y(n)*. The input/output andtaps are all complex.

The normalizing circuits 51,54 receive inputs and feedback from acontrol or other processor and are operable with a fixed pointarithmetic or logic for normalized input and output. For example, ifthere is a 20 dB jammer, the signal coming out of the filter will be afactor of about 100 smaller, and if using fixed-point math precision, itcan be brought back up to obtain more bits and increase the gain of thesamples to work better through the system. The input normalizing circuit51 obtains sample values coming into the filter and attempts to placethem in the proper range for filter fixed-point math functions to workwithout complicating issues.

The amount of normalizing is adjusted from a controller or otherprocessor such that the normalizing function does not modulate databeyond what is desired. This is important depending on the type ofwaveform, such as a M-PSK constellation, constant amplitude waveform, ora M-QAM constellation. The controller or other processor could operatewith a memory function to remember the last gain given to the samplescoming out of the normalizing circuit, including the input and outputnormalizing circuits 51, 54, allowing a small change relative to thesignal. It is possible to allow an automatic gain control (AGC) circuitto make some changes on a sample or block basis. There are somesensitivities to changes in amplitude and the normalizing circuits areoperable that any M-QAM signal having data or information contained inthe amplitude of the waveform is not affected. Any AGC loop could be onboth the memory and the input and output normalizing circuits. Anycontrol signal from a controller or other processor could includeinformation relating to the modulation type and demodulator state.

Overall, the adaptive filter will accomplish better performance if thereis greater spacing between the multipath and the variable delay circuit50 provides such spacing. If only the first tap is used, for example,when the variable delay circuit 50 is not operable, the multipath tendsto group together and the taps can move to a non-zero value if there isan interferer. As illustrated and as noted before, there are three orfour taps in the filter operable to attack three or four interferers. Ifonly one or two taps are desired and used such that the number of tapsare reduced, then the multipath spread introduced by adaptive filter isless since it had to remove fewer interferers or jammers.

It should be understood that as part of the demodulation process, afaster filter update gain can be used for the preamble search andpreamble state of demodulator. The preamble portion of waveform tends tobe less susceptible to waveform variation and to gain variations of theadaptive taps than the data portion of waveform, and thus, once thedemodulator detects a preamble, it could slow down the adaptation rateof filter taps through the feedback mechanism so that the filteradaptation is slower for the data portion of waveform. With feedbackfrom the demodulator, the adaptive filter can adjust the gain of thefilter taps as desired by the state of demodulator.

The automatic tap order selection circuit 52 takes advantage of the factthat there is not necessarily a requirement to use four taps, but three,two or one tap can be used to overcome the disadvantages of a fixedstructure.

Typically, the filters as described can be implemented within a FieldProgrammable Gate Array (FPGA) that is fast enough to implement themodem functions of the waveform. With the improvement in digital signalprocessors, however, various DSP circuits could also be used.

The filter function can be implemented in C code (or assembly language)to establish a narrow band interference (NBI) adaptive filter as eithera FIR or IIR filter. Different variables can be defined, includingchannel buffers, complex demodulation, and power output sums. Filterstate and filter taps are tracked as well as the gain, number of taps,and number of adapted taps. As the filter state is tracked, the outputpower with the adaptive taps is updated.

The C code can define if the modem is in a search mode, for example,searching for a waveform such as a M-QAM, M-PSK or GMSK waveform fortracking the filter. The update gain of the filter can be adjusted basedon the demodulator state. Also, the variable delay is implemented bydefining the number of taps and the number of adaptive taps and thedifference can be the delay between a first fixed tap and the firstadaptive tap. This can be implemented in C code, for example. The filterstate values can be shuffled to make room for a next input. The C codecan also define the output power relative to the input power to allowinterference reduction and automatically select the filter operation bybypassing into the output or through the filter using the switch.

FIG. 3 is an adaptive filter system 200 having four adaptive filters202, 204, 206, and 208 positioned parallel. The first adaptive filter202 has one adaptive tap. The second adaptive filter 204 has twoadaptive taps. The third adaptive filter 206 has three adaptive taps.The fourth adaptive filter 208 has four adaptive taps. A power measuringcircuit 209 measures the input power. Each adaptive filter has arespective power measuring circuit 210, 212, 214, and 216 withappropriate feedback of the type as mentioned relative to FIG. 2. Theadaptive filters and power measuring circuit are shown in basicdiagrammatic view only. Each power measuring circuit is output into aselection circuit 220 for final output. The received signal is inputinto each adaptive filter. The selection circuit 220 senses the outputpower from each adaptive filter and selects the adaptive filter with themost suppression or smallest output power as the adaptive filter to useas the output in the circuit 200.

FIGS. 4-9 are various graphs that were generated to show the effect ofgain values and the number of taps on the performance of the adaptivefilter and its effect on a demodulated waveform. These graphs show theeffects of these parameters and the trade offs that are required. TheNBI or adaptive filter as explained before is established to trackinterferers that are changing in frequency or turning on/off. A fasterfilter introduces more noise, and thus this type of filter would berequired only for more robust waveforms such that the tracking speed ofthe adaptive filter is improved by knowing the modulation. Also, thefewer taps in the adaptive filter, the faster the adaptive filter canadapt to the interferer but the fewer interferers it can handle. Thesegraphs can illustrate this problem and solution.

FIGS. 4A, 4B and 4C are graphs showing the effect of the update gain onGaussian noise input in which FIG. 4A shows the gain at ½⁷, FIG. 4Bshows the gain at ½³, and FIG. 4C shows the gain at ½¹⁰. Ten thousand(10,000) iterations with the last one thousand (1,000) are displayed.The Gaussian noise input will force the taps to train to zero and theamount of variability is a function of the update gain. The first filtertap is typically a one, and as a result, the plus (+) sign at the rightportion of the graph is fixed at around 4,096 for the fixed-pointsimulation. The scattering around zero pertain to the four taps of theadaptive filter. There is excessive moving of the taps as shown when thegain is ½³. The graph shows that the variable adaptive gain and updateaffects the waveform. When the gain is ½⁷, the error of the signal isslowing, making it smaller by 1/16. The gain of 3, as shown in FIG. 4B,is operative as ⅛ and the filter functions to take the output error anddivide it by 8. The signal error is fed as the adaptive tap. If the gainof 3 is left for demodulation, the taps will change too much. Asillustrated in FIG. 4C, the gain of ½¹⁰ offers the best performance andthe taps move very little.

It should be understood that if there is an interferer or jammerpresent, the filter should be able to adapt quickly. A gain of ½¹⁰ isslow, but there is still a trade-off for how fast the system can adapt.

FIGS. 5A, 5B and 5C show the effect of the update gain on Gaussian noiseplus a tone (20 dB) input. The tone could correspond to a carrier. Asshown by the results in these graphs, when there is a gain of ½⁷ and½¹⁰, there is little difference, and thus, the gain of ½⁷ would probablybe sufficient since the gain of ½¹⁰ would adapt much slower than ½⁷.With the gain of ½³, the taps are still moving around excessively, andthus, the gain of ½³ would not be desired. The graph results show thatthe taps with the gain of ½³ are in a different location than theupdated gains of ½⁷ and ½¹⁰. Once the system adapts to the gain of ½⁷ asshown in FIG. 5A, the system typically stays fixed. The filter operatingat the gain of ½¹⁰ would be excessively slow as compared to the filteroperative with the gain of ½⁷ and not as desirable.

FIGS. 6A, 6B and 6C show the effect of the update gain on a GMSK signalinput with the GMSK by itself. The gain of ½³ is poor, but the gain of½¹⁰ is better than the gain of ½⁷, and thus, is desired.

FIGS. 7A, 7B and 7C show the effect of the update gain on the GMSK plusa tone (20 dB) input and showing that the gain of ½⁷ is advantageous andmore efficient than the gain of ½¹⁰. The gain of ½³ still shows the tapsmoving excessively.

FIG. 8 is a graph showing the effect of the update gain on the GMSK plusthe tone (20 dB) input signal and showing the settling time with anupdated gain shown in the graph for the narrow band interference (NBI)output power as an NBI filter. The graph displays the adaptation resultsand how long it takes to obtain a smaller output power, indicating thatthe NBI FIR filter is removing the jammer or interferer. With anadaptation of ½¹⁰ (as 1/1024), it has taken a longer time to obtain thegoal. The update gain of ½³ shows that it is quick, but there is extranoise. The update gain of ½⁷ shows the system is quick with less noise.The adaptation rates depend on the state of the modem. The update gainof ½³ would take out the jammer quickly. If the power at the input andoutput change, then the adaptation can be slowed. Thus, the systemperformance can be improved by monitoring the power at the output,monitoring the adaptation, and monitoring the state of the modem.

FIGS. 9A, 9B, 9C and 9D show the effect of the number of adaptive tapson the GMSK plus the tone (20 dB) input with different suppression atdifferent decibel (dB) ranges. For example, if there is not a largeinterferer, it may be necessary to use fewer taps, for example, only twotaps at 15 dB. If there is a larger interferer, then more taps would bedesirable. The filter provides an intelligent manner to manage thenumber of taps.

Overall the system provides multiple delay taps and a variable delay atthe front-end such that the first few taps do not have to be used whiledifferent delays can be used. A “one” can be used for the first filtertap and some filter taps can be skipped. The output power can bemonitored as noted before such that the filter determines which branchto use and whether the input signal should be bypassed directly tooutput into the filter. The filter can operate with different filtertaps, for example, a filter with 1, 2, 3 or 4 taps, while the poweroutput can be monitored to determine which branch to use as notedbefore. The gain of the filter can be adapted based on whether thesystem is searching such as for a waveform and whether the system is ina preamble mode or data mode and whether a certain modulation is used.Depending on the type of signal constellation used to transmit data,much of the transmitted information is in the phase and not theamplitude (i.e. M-PSK), and thus, the system would be less likely to behurt by faster filter update gains. If the system knows it will receivea M-QAM constellation, it could consider slowing the filter update gainand increase normalizing circuit memory after the preamble, and thus,the system can exploit what knowledge it has.

For purposes of description, some background information on coding,interleaving, and an exemplary wireless, mobile radio communicationssystem that includes ad-hoc capability and can be modified for use isset forth. This example of a communications system that can be used andmodified for use with the present invention is now set forth with regardto FIGS. 10 and 11.

An example of a radio that could be used with such system and method isa Falcon™ III radio manufactured and sold by Harris Corporation ofMelbourne, Fla. This type of radio can support multiple wavebands form30 MHz up to 2 GHz, including L-band SATCOM and MANET. The waveforms canprovide secure IP data networking. It should be understood thatdifferent radios can be used, including software defined radios that canbe typically implemented with relatively standard processor and hardwarecomponents. One particular class of software radio is the Joint TacticalRadio (JTR), which includes relatively standard radio and processinghardware along with any appropriate waveform software modules toimplement the communication waveforms a radio will use. JTR radios alsouse operating system software that conforms with the softwarecommunications architecture (SCA) specification (seewww.jtrs.saalt.mil), which is hereby incorporated by reference in itsentirety. The SCA is an open architecture framework that specifies howhardware and software components are to interoperate so that differentmanufacturers and developers can readily integrate the respectivecomponents into a single device.

The Joint Tactical Radio System (JTRS) Software Component Architecture(SCA) defines a set of interfaces and protocols, often based on theCommon Object Request Broker Architecture (CORBA), for implementing aSoftware Defined Radio (SDR). In part, JTRS and its SCA are used with afamily of software re-programmable radios. As such, the SCA is aspecific set of rules, methods, and design criteria for implementingsoftware re-programmable digital radios.

The JTRS SCA specification is published by the JTRS Joint Program Office(JPO). The JTRS SCA has been structured to provide for portability ofapplications software between different JTRS SCA implementations,leverage commercial standards to reduce development cost, reducedevelopment time of new waveforms through the ability to reuse designmodules, and build on evolving commercial frameworks and architectures.

The JTRS SCA is not a system specification, as it is intended to beimplementation independent, but a set of rules that constrain the designof systems to achieve desired JTRS objectives. The software framework ofthe JTRS SCA defines the Operating Environment (OE) and specifies theservices and interfaces that applications use from that environment. TheSCA OE comprises a Core Framework (CF), a CORBA middleware, and anOperating System (OS) based on the Portable Operating System Interface(POSIX) with associated board support packages. The JTRS SCA alsoprovides a building block structure (defined in the API Supplement) fordefining application programming interfaces (APIs) between applicationsoftware components.

The JTRS SCA Core Framework (CF) is an architectural concept definingthe essential, “core” set of open software Interfaces and Profiles thatprovide for the deployment, management, interconnection, andintercommunication of software application components in embedded,distributed-computing communication systems. Interfaces may be definedin the JTRS SCA Specification. However, developers may implement some ofthem, some may be implemented by non-core applications (i.e., waveforms,etc.), and some may be implemented by hardware device providers.

For purposes of description only, a brief description of an example of acommunications system that includes communications devices thatincorporate the filter in accordance with a non-limiting example, isdescribed relative to a non-limiting example shown in FIG. 10. Thishigh-level block diagram of a communications system includes a basestation segment and wireless message terminals that could be modifiedfor use with the present invention. The base station segment includes aVHF radio 60 and HF radio 62 that communicate and transmit voice or dataover a wireless link to a VHF net 64 or HF net 66, each which include anumber of respective VHF radios 68 and HF radios 70, and personalcomputer workstations 72 connected to the radios 68,70. Ad-hoccommunication networks 73 are interoperative with the various componentsas illustrated. The entire network can be ad-hoc and include source,destination and neighboring mobile nodes. Thus, it should be understoodthat the HF or VHF networks include HF and VHF net segments that areinfrastructure-less and operative as the ad-hoc communications network.Although UHF and higher frequency radios and net segments are notillustrated, these could be included.

The radio can include a demodulator circuit 62 a and appropriateconvolutional encoder circuit 62 b, block interleaver 62 c, datarandomizer circuit 62 d, data and framing circuit 62 e, modulationcircuit 62 f, matched filter circuit 62 g, block or symbol equalizercircuit 62 h with an appropriate clamping device, deinterleaver anddecoder circuit 62 i modem 62 j, and power adaptation circuit 62 k asnon-limiting examples. A vocoder circuit 62 l can incorporate the decodeand encode functions and a conversion unit could be a combination of thevarious circuits as described or a separate circuit. A clock circuit 62m can establish the physical clock time and through second ordercalculations as described below, a virtual clock time. The network canhave an overall network clock time. These and other circuits operate toperform any functions necessary for the present invention, as well asother functions suggested by those skilled in the art. Other illustratedradios, including all VHF (or UHF) and higher frequency mobile radiosand transmitting and receiving stations can have similar functionalcircuits. Radios could range from 30 MHz to about 2 GHz as non-limitingexamples.

The base station segment includes a landline connection to a publicswitched telephone network (PSTN) 80, which connects to a PABX 82. Asatellite interface 84, such as a satellite ground station, connects tothe PABX 82, which connects to processors forming wireless gateways 86a, 86 b. These interconnect to the VHF radio 60 or HF radio 62,respectively. The processors are connected through a local area networkto the PABX 82 and e-mail clients 90. The radios include appropriatesignal generators and modulators.

An Ethernet/TCP-IP local area network could operate as a “radio” mailserver. E-mail messages could be sent over radio links and local airnetworks using STANAG-5066 as second-generation protocols/waveforms, thedisclosure which is hereby incorporated by reference in its entiretyand, of course, preferably with the third-generation interoperabilitystandard: STANAG-4538, the disclosure which is hereby incorporated byreference in its entirety. An interoperability standard FED-STD-1052,the disclosure which is hereby incorporated by reference in itsentirety, could be used with legacy wireless devices. Examples ofequipment that can be used in the present invention include differentwireless gateway and radios manufactured by Harris Corporation ofMelbourne, Fla. This equipment could include RF5800, 5022, 7210, 5710,5285 and PRC 117 and 138 series equipment and devices as non-limitingexamples.

These systems can be operable with RF-5710A high-frequency (HF) modemsand with the NATO standard known as STANAG 4539, the disclosure which ishereby incorporated by reference in its entirety, which provides fortransmission of long distance radio at rates up to 9,600 bps. Inaddition to modem technology, those systems can use wireless emailproducts that use a suite of data-link protocols designed and perfectedfor stressed tactical channels, such as the STANAG 4538 or STANAG 5066,the disclosures which are hereby incorporated by reference in theirentirety. It is also possible to use a fixed, non-adaptive data rate ashigh as 19,200 bps with a radio set to ISE mode and an HF modem set to afixed data rate. It is possible to use code combining techniques andARQ.

A communications system that incorporates communications devices can beused in accordance with non-limiting examples of the present inventionand is shown in FIG. 11. A transmitter is shown at 91 and includes basicfunctional circuit components or modules, including a forward errorcorrection encoder 92 a that includes a puncturing module, which couldbe integral to the encoder or a separate module. The decoder 92 a andits puncturing module includes a function for repeating as will beexplained below. Encoded data is interleaved at an interleaver 92 b, forexample, a block interleaver, and in many cases modulated at modulator92 c. This modulator can map the communications data into differentsymbols based on a specific mapping algorithm to form a communicationssignal. For example, it could form Minimum Shift Keying or GaussianMinimum Shift Keying (MSK or GMSK) symbols. Other types of modulationcould be used in accordance with non-limiting examples of the presentinvention. Up-conversion and filtering occurs at an up-converter andfilter 92 d, which could be formed as an integrated module or separatemodules. Communications signals are transmitted, for example, wirelesslyto receiver 93.

At the receiver 93, down conversion and filtering occurs at a downconverter and filter 94 a, which could be integrated or separatemodules. The signal is demodulated at demodulator 94 b and deinterleavedat deinterleaver 94 c. The deinterleaved data (i.e. bit soft decisions)is decoded and depunctured (for punctured codes), combined (for repeatedcodes) and passed through (for standard codes) at decoder 94 d, whichcould include a separate or integrated depuncturing module. The system,apparatus and method can use different modules and different functions.These components as described could typically be contained within onetransceiver.

It should be understood, in one non-limiting aspect of the presentinvention, a rate ½, K=7 convolutional code can be used as an industrystandard code for forward error correction (FEC) during encoding. Forpurposes of understanding, a more detailed description of basiccomponents now follows. A convolutional code is an error-correctingcode, and usually has three parameters (n, k, m) with n equal to thenumber of output bits, k equal to the number of input bits, and m equalto the number of memory registers, in one non-limiting example. Thequantity k/n could be called the code rate with this definition and is ameasure of the efficiency of the code. K and n parameters can range from1 to 8, m can range from 2 to 10, and the code rate can range from ⅛ to⅞ in non-limiting examples. Sometimes convolutional code chips arespecified by parameters (n, k, L) with L equal to the constraint lengthof the code as L=k (m−1). Thus, the constraint length can represent thenumber of bits in an encoder memory that would affect the generation ofn output bits. Sometimes the letters may be switched depending on thedefinitions used.

The transformation of the encoded data is a function of the informationsymbols and the constraint length of the code. Single bit input codescan produce punctured codes that give different code rates. For example,when a rate ½ code is used, the transmission of a subset of the outputbits of the encoder can convert the rate ½ code into a rate ⅔ code.Thus, one hardware circuit or module can produce codes of differentrates. Punctured codes allow rates to be changed dynamically throughsoftware or hardware depending on channel conditions, such as rain orother channel impairing conditions.

An encoder for a convolutional code typically uses a look-up table forencoding, which usually includes an input bit as well as a number ofprevious input bits (known as the state of the encoder), the table valuebeing the output bit or bits of the encoder. It is possible to view theencoder function as a state diagram, a tree diagram or a trellisdiagram.

Decoding systems for convolutional codes can use 1) sequential decoding,or 2) maximum likelihood decoding, also referred to as Viterbi decoding,which typically is more desirable. Sequential decoding allows bothforward and backward movement through the trellis. Viterbi decoding asmaximum likelihood decoding examines a receive sequence of given length,computes a metric for each path, and makes a decision based on themetric.

Puncturing convolutional codes is a common practice in some systems andis used in accordance with non-limiting examples of the presentinvention. It should be understood that in some examples a puncturedconvolutional code is a higher rate code obtained by the periodicelimination of specific code bits from the output of a low rate encoder.Punctured convolutional code performance can be degraded compared withoriginal codes, but typically the coding rate increases.

Some of the basic components that could be used as non-limiting examplesof the present invention include a transmitter that incorporates aconvolutional encoder, which encodes a sequence of binary input vectorsto produce the sequence of binary output vectors and can be definedusing a trellis structure. An interleaver, for example, a blockinterleaver, can permute the bits of the output vectors. The interleaveddata would also be modulated at the transmitter (by mapping to transmitsymbols) and transmitted. At a receiver, a demodulator demodulates thesignal.

A block deinterleaver recovers the bits that were interleaved. A Viterbidecoder could decode the deinterleaved bit soft decisions to producebinary output data.

Often a Viterbi forward error correction module or core is used thatwould include a convolutional encoder and Viterbi decoder as part of aradio transceiver as described above. For example if the constraintlength of the convolutional code is 7, the encoder and Viterbi decodercould support selectable code rates of ½, ⅔, ¾, ⅘, ⅚, 6/7, ⅞ usingindustry standard puncturing algorithms.

Different design and block systems parameters could include theconstraint length as a number of input bits over which the convolutionalcode is computed, and a convolutional code rate as the ratio of theinput to output bits for the convolutional encoder. The puncturing ratecould include a ratio of input to output bits for the convolutionalencoder using the puncturing process, for example, derived from a rate ½code.

The Viterbi decoder parameters could include the convolutional code rateas a ratio of input to output bits for the convolutional encoder. Thepuncture rate could be the ratio of input to output bits for theconvolutional encoder using a puncturing process and can be derived froma rate ½ mother code. The input bits could be the number of processingbits for the decoder. The Viterbi input width could be the width ofinput data (i.e. soft decisions) to the Viterbi decoder. A metricregister length could be the width of registers storing the metrics. Atrace back depth could be the length of path required by the Viterbidecoder to compute the most likely decoded bit value. The size of thememory storing the path metrics information for the decoding processcould be the memory size. In some instances, a Viterbi decoder couldinclude a First-In/First-Out (FIFO) buffer between depuncture andViterbi function blocks or modules. The Viterbi output width could bethe width of input data to the Viterbi decoder.

The encoder could include a puncturing block circuit or module as notedabove. Usually a convolutional encoder may have a constraint length of 7and take the form of a shift register with a number of elements, forexample, 6. One bit can be input for each clock cycle. Thus, the outputbits could be defined by a combination of shift register elements usinga standard generator code and be concatenated to form an encoded outputsequence. There could be a serial or parallel byte data interface at theinput. The output width could be programmable depending on the puncturedcode rate of the application.

A Viterbi decoder in non-limiting examples could divide the input datastream into blocks, and estimate the most likely data sequence. Eachdecoded data sequence could be output in a burst. The input andcalculations can be continuous and require four clock cycles for everytwo bits of data in one non-limiting example. An input FIFO can bedependent on a depuncture input data rate.

It should also be understood that the present invention is not limitedto convolutional codes and similar FEC, but also turbo codes could beused as high-performance error correction codes or low-densityparity-check codes that approach the Shannon limit as the theoreticallimit of maximum information transfer rate over a noisy channel. Thus,some available bandwidth can be increased without increasing the powerof the transmission. Instead of producing binary digits from the signal,the front-end of the decoder could be designed to produce a likelihoodmeasure for each bit.

The system and FIR filter, in accordance with non-limiting examples ofthe present invention, can be used in multiprocessor embedded systemsand related methods and also used for any type of radio softwarecommunications architecture as used on mainframe computers or smallcomputers, including laptops with an added transceiver, such as used bymilitary and civilian applications, or in a portable wirelesscommunications device 120 as illustrated in FIG. 12. The portablewireless communications device is illustrated as a radio that caninclude a transceiver as an internal component and handheld housing 122with an antenna 124 and control knobs. A Liquid Crystal Display (LCD) orsimilar display can be positioned on the housing in an appropriatelocation for display. The various internal components, including dualprocessor systems for red and black subsystems and software that isconforming with SCA, is operative with the illustrated radio. Although aportable or handheld radio is disclosed, the architecture as describedcan be used with any processor system operative with the system inaccordance with non-limiting examples of the present invention. Anexample of a communications device that could incorporate the adaptivefilter, in accordance with non-limiting examples of the presentinvention, is the Falcon® III manpack or tactical radio platformmanufactured by Harris Corporation of Melbourne, Fla.

This application is related to copending patent applications entitled,“COMMUNICATIONS SYSTEM USING ADAPTIVE FILTER FOR INTERFERENCEREDUCTION,” and “COMMUNICATIONS SYSTEM USING ADAPTIVE FILTER THAT ISSELECTED BASED ON OUTPUT POWER,” and “COMMUNICATIONS SYSTEM USINGADAPTIVE FILTER AND SELECTED ADAPTIVE FILTER TAPS,” and “COMMUNICATIONSSYSTEM USING ADAPTIVE FILTER WITH ADAPTIVE UPDATE GAIN,” and“COMMUNICATIONS SYSTEM USING ADAPTIVE FILTER WITH NORMALIZATIONCIRCUIT,” and “COMMUNICATIONS SYSTEM USING ADAPTIVE FILTER AND VARIABLEDELAY BEFORE ADAPTIVE FILTER TAPS,” which are filed on the same date andby the same assignee and inventors, the disclosures which are herebyincorporated by reference.

Many modifications and other embodiments of the invention will come tothe mind of one skilled in the art having the benefit of the teachingspresented in the foregoing descriptions and the associated drawings.Therefore, it is understood that the invention is not to be limited tothe specific embodiments disclosed, and that modifications andembodiments are intended to be included within the scope of the appendedclaims.

That which is claimed is:
 1. A communications system for receiving amodulated communications signal that carries encoded communicationsdata, comprising: a signal input that receives the communicationssignal; an adaptive filter circuit connected to the signal input andcomprising a plurality of parallel adaptive filters, each havingnon-adaptive and adaptive filter taps with weighted coefficients thatare different in number from the respective other parallel adaptivefilters within the adaptive filter circuit and a selection outputcircuit connected to each adaptive filter that selects for output theadaptive filter having one of at least the most suppression and theleast output power; a tap order selection circuit connected to saidplurality of adaptive filter taps and configured to select a number andorder of adaptive filter taps based on filter performance andmodulation; a demodulator for demodulating the received signal afterfiltering; and a decoder that receives the filtered output signal fromthe demodulator and decodes the signal to obtain the communicationsdata.
 2. The communications system according to claim 1 wherein eachadaptive filter comprises a power measuring circuit for measuring thepower output from each adaptive filter and the power input to eachadaptive filter.
 3. The communications system according to claim 1,wherein said adaptive filters have an increasing number of adaptive tapsstarting from a first adaptive filter having one adaptive tap, the nextadaptive filter having two adaptive taps, up to N adaptive taps for thenth adaptive filter.
 4. The communications system according to claim 1,wherein at least one of said adaptive filters includes an input and/oroutput normalizing circuit that obtains sample values from a receivedsignal input to the adaptive filter or output by the adaptive filter toincrease gain recovery based on type of modulation used by communicationsystem, demodulator state such as preamble search, preamble detected anddata state and/or other signal acquisition information.
 5. Thecommunications system according to claim 1, wherein at least one of saidadaptive filters includes an interference reduction circuit responsiveto one of at least the receive state of a demodulator and the type ofmodulation used by communication system and the measured input power toadaptive filter and the measured output power of adaptive filter forupdating the adaptive gain of the adaptive filter, separating thespacing of the multipath introduced by adaptive filter into system, andbypassing the adaptive filter to an output.
 6. The communications systemaccording to claim 1, wherein at least one of said adaptive filtersincludes a variable delay circuit operative before the adaptive filtertaps for separating the spacing of multipath introduced by adaptivefilter into system and producing a filtered output signal with improvedmultipath performance and reduction of narrowband interference.
 7. Thecommunications system according to claim 1, wherein at least one of saidadaptive filters includes an adaptive gain circuit for updating theadaptive gain of the adaptive filter responsive to a receive state of ademodulator or the type of modulation used by communication system. 8.The communications system according to claim 1, wherein at least one ofsaid adaptive filters is selected to pass its output to the demodulatorbased on the measured input power to the adaptive filter and themeasured output power of the adaptive filter.
 9. An adaptive filtercircuit, comprising: a signal input that receives a sampled input signalhaving communications data encoded therein; a plurality of paralleladaptive filters each having non-adaptive and adaptive filter taps withweighted coefficients that are different in number from the respectiveother parallel adaptive filters; a selection output circuit connected toeach adaptive filter that selects for output the adaptive filter havingone of at least the most suppression and the least output power; and atap order selection circuit connected to said plurality of adaptivefilter taps and configured to select a number and order of adaptivefilter taps based on filter performance and modulation.
 10. The adaptivefilter according to claim 9, wherein each adaptive filter comprises apower measuring circuit or circuits for measuring the power input to oroutput from each adaptive filter.
 11. The adaptive filter according toclaim 9, wherein said adaptive filters have an increasing number ofadaptive taps starting with a first adaptive filter having one adaptivetap, the next adaptive filter having two adaptive taps, up to N adaptivetaps for the nth adaptive filter.
 12. The adaptive filter according toclaim 9, wherein at least one of said adaptive filters includes an inputand/or output normalizing circuit that obtains sample values from areceived signal input to the adaptive filter or output by the adaptivefilter to increase gain recovery based on type of modulation used bycommunication system, demodulator state such as preamble search,preamble detected and data state and/or other signal acquisitioninformation.
 13. The adaptive filter according to claim 9, wherein atleast one of said adaptive filters includes an interference reductioncircuit responsive to one of at least the receive state of ademodulator, the type of modulation used by communication system, themeasured input power to filters and the measured output power of filtersfor updating the adaptive gain of the adaptive filter, separating thespacing of the multipath introduced by adaptive filter, controllinginput and output normalizing circuits and bypassing the adaptive filterto an output.
 14. The adaptive filter according to claim 9, wherein atleast one of said adaptive filters includes a variable delay circuitoperative before the adaptive filter taps for separating the spacing ofmultipath introduced by adaptive filter and producing a filtered outputsignal with improved multipath performance and reduction of narrowbandinterference.
 15. The adaptive filter according to claim 9, wherein atleast one of said adaptive filters includes an adaptive gain circuit forupdating the adaptive gain of the adaptive filter responsive to areceive state of a demodulator or the type of modulation used bycommunication system.
 16. The communications system according to claim9, wherein at least one of said adaptive filters includes an inputand/or output normalizing circuit that obtains sample values from areceived signal input to the adaptive filter or output by the adaptivefilter to increase gain recovery based on type of modulation used bycommunication system, demodulator state such as preamble search,preamble detected and data state and/or other signal acquisitioninformation.
 17. The adaptive filter according to claim 9, wherein atleast one of said adaptive filters is selected to pass its output to thedemodulator based on the measured input power to the adaptive filter andthe measured output power of the adaptive filter.
 18. A method ofcommunicating, comprising: receiving a modulated signal that carriesencoded communications data; filtering the signal within an adaptivefilter circuit comprising a plurality of adaptive filters each having aplurality of non-adaptive and adaptive filter taps with weightedcoefficients that are different in number from the respective otherparallel adaptive filters within the adaptive filter circuit; selectinga number and order of adaptive filter taps based on filter performanceand modulation using a tap order selection circuit connected to theadaptive filter taps; and outputting a filtered signal from the adaptivefilter having the most suppression or least output power.
 19. The methodaccording to claim 18, which further comprises measuring the poweroutput from each adaptive filter and selecting the adaptive filterhaving the least output power.
 20. The method according to claim 18,which further comprises forming the adaptive filter circuit such thatthe adaptive filters have an increasing number of adaptive taps startingwith a first adaptive filter having one adaptive tap, the next adaptivefilter having two adaptive taps, up to N adaptive taps for the nthadaptive filter.
 21. The method according to claim 18, which furthercomprises an input and/or output normalizing circuit that obtains samplevalues from a received signal input to the adaptive filter or output bythe adaptive filter to increase gain recovery based on type ofmodulation used by communication system, demodulator state such aspreamble search, preamble detected and data state and/or other signalacquisition information.
 22. The method according to claim 18, whichfurther comprises updating the adaptive gain of each adaptive filter,separating the spacing of the multipath introduced by each adaptivefilter, and bypassing the adaptive filter to an output responsive to oneof at least the measured power at the input to the adaptive filter, themeasured power at the output of the adaptive filter, the demodulatorstate and the type of modulation used by the communication system. 23.The method according to claim 18, which further comprises separating thespacing of multipath introduced by adaptive filter and producing afiltered output signal with improved multipath performance and reductionof narrowband interference within a variable delay circuit.
 24. Themethod according to claim 18, which further comprises updating theadaptive gain of the adaptive filter responsive to a receive state of ademodulator and/or the type of modulation used by communication system.25. A communications system for receiving a modulated communicationssignal that carries encoded communications data, comprising: a signalinput that receives the communications signal; an adaptive filtercircuit connected to the signal input and comprising a plurality ofparallel adaptive filters, each having non-adaptive and adaptive filtertaps with weighted coefficients that are different in number from therespective other parallel adaptive filters within the adaptive filtercircuit; a selection output circuit connected to each adaptive filterthat selects for output the adaptive filter having one of at least themost suppression and the least output power; a demodulator fordemodulating the received signal after filtering; a decoder thatreceives the filtered output signal from the demodulator and decodes thesignal to obtain the communications data; and wherein at least one ofsaid adaptive filters includes a variable delay circuit operative beforethe adaptive filter taps for separating the spacing of multipathintroduced by adaptive filter into system and producing a filteredoutput signal with improved multipath performance and reduction ofnarrowband interference.
 26. An adaptive filter circuit, comprising: asignal input that receives a sampled input signal having communicationsdata encoded therein; a plurality of parallel adaptive filters eachhaving non-adaptive and adaptive filter taps with weighted coefficientsthat are different in number from the respective other parallel adaptivefilters; a selection output circuit connected to each adaptive filterthat selects for output the adaptive filter having one of at least themost suppression and the least output power; and wherein at least one ofsaid adaptive filters includes a variable delay circuit operative beforethe adaptive filter taps for separating the spacing of multipathintroduced by adaptive filter and producing a filtered output signalwith improved multipath performance and reduction of narrowbandinterference.
 27. A method of communicating, comprising: receiving amodulated signal that carries encoded communications data; filtering thesignal within an adaptive filter circuit comprising a plurality ofadaptive filters each having a plurality of non-adaptive and adaptivefilter taps with weighted coefficients that are different in number fromthe respective other parallel adaptive filters within the adaptivefilter circuit; outputting a filtered signal from the adaptive filterhaving the most suppression or least output power; and separating thespacing of multipath introduced by adaptive filter and producing afiltered output signal with improved multipath performance and reductionof narrowband interference within a variable delay circuit.